Inheritance of Resistance to Pathotypes QCC and MCC ofPuccinia graminisf. sp.triticiin Barley Line Q21861 and Temperature Effects on the Expression of Resistance

Barley line Q21861 is one of several accessions that possess resistance to pathotypes QCC and MCC of Puccinia graminis f. sp. tritici. Crosses were made between Q21861 and several barley cultivars to study the inheritance of resistance to pathotypes QCC and MCC. Progeny evaluations indicated that resistance to pathotype QCC in Q21861 was conferred by a recessive gene that conditioned low infection types at low incubation temperatures (18-20 C). This gene was ineffective against pathotype QCC at incubation temperatures greater than 27 C. Resistance to pathotype MCC in Q21861 was controlled by two genes, one dominant and one recessive, that segregated independently. The dominant gene is allelic to Rpg 1, and the recessive gene identified is the same one conferring resistance to pathotype QCC. This recessive gene is not allelic with Rpg2 based on an allelism test. It is unlikely allelic with Rpg3 based on reaction to pathotype QCC at the seedling stage, a recessive inheritance pattern, and temperature sensitivity. The locus and allele symbols Rpg4 and rpg4d, respectively, are suggested for the recessive gene in Q21861.